Abstract: Most of the second distal clastic gas pools in the West Sichuan depression are the composite structural and lithologic traps. The efficiency and sizes of the gas pools are controlled by the combined factors of structural morphology, tectonic position of faults and distribution of the reservoir rocks. Only when the reservoir rocks are connected with the faults as the channels of gas migration at the lower levels, or constitute the structural and/or lithologic seals along their dip direction, may the traps become effective.